Chair base



The design is embodied in the chair base.

FIG. 1 is an isometric view of the chair base showing the new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a left side elevation view thereof; and,

FIG. 7 is a right side elevation view thereof.

The broken lines shown in the views are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a chair base, as shown and described. 